Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 140236 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 936 PM EST Wed Dec 13 2017 .SYNOPSIS... An Alberta Clipper will pass nearby tonight through early Thursday. Developing low pressure will pass off the east coast late Friday and high pressure will return for Saturday. Low pressure may impact the area early next week. && .NEAR TERM /THROUGH THURSDAY/... Band of very light snow went through our local area here in northern VA about an hour or two ago producing only a trace. Snow has shifted north and east into Baltimore and northeast MD where a few snow reports up to half inch have been received. After 06Z, all snow is expected to shift well north into Pennsylvania with snow ending except in the upslope areas of far western MD and eastern WV. Becoming breezy again late tonight into early Thu and windy over the mtns where gusts could reach wind advisory criteria. Breezy again tomorrow with highs only in the 30s and wind gusts up to 35 mph in the morning diminishing in the afternoon. && .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... Weak high pressure crosses the region Thursday night into early Friday, with partial clearing and dry conditions with lighter winds. Trough passing aloft however will generate a surface low off the East Coast. While the chance of this low affecting our region remains small, with the trough crossing the region have kept slight chance to low chance pops for snow showers over the region. Highs will cool a bit with the passing trough, with 30s generally expected. System heads east of the region at night, with drying likely, except for the upslope areas, where accumulations are likely. Lows will be below freezing once again. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... By Saturday, the upper level pattern will begin to change, with upper level troughing pulling away to the northeast due to developing ridging downstream of a west coast trough. Surface high pressure will be building into the area, although temperatures may remain slightly below normal in continued northwest flow. The high will begin to move to the east on Sunday, which will allow a more southerly flow to develop with warmer temperatures. For the remainder of the long term, while there is moderate model agreement on the large scale pattern, there are considerable smaller scale differences. One shortwave trough will be crossing late Sunday, with deeper troughing digging toward the eastern United States in the Tuesday to Wednesday time frame. These two time frames represent the best opportunity for some precipitation, although with low confidence due to the spread in timing, locations and moisture sources. With a milder westerly flow aloft overall, temperatures should remain above normal (even above freezing at night), so any precipitation should be in the form of rain, except minimal chances for upslope snow. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... VFR conditions at present have an increasing chance of deteriorating this evening as a brief period of snow is looking more and more likely at the terminals near and north of DC. Cigs and vis are likely to drop to at least MVFR at BWI/MTN/MRB, and quite possibly doing likewise at DCA/IAD. CHO is most likely to stay VFR. Conditions should improve after midnight and generallye expect VFR to dominate Thursday through Friday night, though the risk of snow showers will be elevated again on Friday as another weak system crosses the area. Winds will relax tonight but become reinvigorated from the northwest on Thursday. VFR with high pressure for Saturday and most of Sunday. A weak weather system could bring some showers late Sunday into Monday, but it`s uncertain at this time if sub-VFR conditions would result. && .MARINE... Gale warning has been issued for the lower waters through 17Z Thu. Marginal gusts up to 35 kt possible. SCA elsewhere through Thu afternoon. We then drop back below SCA over the course of Thursday night, but another system crossing the area could bring SCA back on Friday. Small Craft Advisory conditions will remain possible through Saturday in west/northwest flow. Winds will become lighter Saturday night into Sunday with high pressure. Southerly flow on Sunday will become westerly on Monday as a weak system passes. At this time, it appears winds will remain below criteria through this period. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Winter Weather Advisory until 7 AM EST Thursday for MDZ501. VA...None. WV...Winter Weather Advisory until 7 AM EST Thursday for WVZ501-503. MARINE...Small Craft Advisory until midnight EST Thursday night for ANZ531>533-537-539>541. Small Craft Advisory until 6 PM EST Thursday for ANZ530-535- 536-538-542. Small Craft Advisory from 6 PM Thursday to midnight EST Thursday night for ANZ534-543. Gale Warning until noon EST Thursday for ANZ534-543. && $$ SYNOPSIS...RCM NEAR TERM...LFR SHORT TERM...RCM LONG TERM...ADS AVIATION...ADS/RCM MARINE...ADS/RCM is the U.S. government's official web portal to all federal, state and local government web resources and services.